Browsing by Subject "disturbance dynamics"

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  • Kivinen, Sonja; Nummi, Petri; Kumpula, Timo (2020)
    Beavers (Castorsp.) are ecosystem engineers that cause significant changes to their physical environment and alter the availability of resources to other species. We studied flood dynamics created by American beaver (C. canadensisK.) in a southern boreal landscape in Finland in 1970-2018. We present for the first time, to our knowledge, a temporally continuous long-term study of beaver-induced flood disturbances starting from the appearance of beaver in the area. During the 49 years, the emergence of new sites flooded by beaver and repeated floods (61% of the sites) formed a dynamic mosaic characterized by clustered patterns of beaver sites. As beaver dispersal proceeded, connectivity of beaver sites increased significantly. The mean flood duration was approximately three years, which highlights the importance of datasets with high-temporal resolution in detecting beaver-induced disturbances. An individual site was often part of the active flood mosaic over several decades, although the duration and the number of repeated floods at different sites varied considerably. Variation of flood-inundated and post-flood phases at individual sites resulted in a cumulative number of unique patches that contribute to environmental heterogeneity in space and time. A disturbance mosaic consisting of patches differing by successional age and flood history is likely to support species richness and abundance of different taxa and facilitate whole species communities. Beavers are thus a suitable means to be used in restoration of riparian habitat due to their strong and dynamic influence on abiotic environment and its biotic consequences.
  • Kilpinen, Satu (Helsingin yliopisto, 2018)
    Increasing human impact has radically changed the forest structure and depleted the area of natural forests in many regions. In spite of active natural forest research during the last decades, the current knowledge on the southern boreal region, deciduous and mixed forests fall short. The knowledge on natural forests can be utilized for planning sustainable forestry, conservation measures or in environmental impact assessments regarding human influence on forests. The natural disturbance dynamics can be used as a model in silviculture, for example in the planning of restoration activities or commercial forest cuttings. The underlying presumption is that emulating natural forest dynamics can help to preserve such values as the forest biodiversity or resilience. In this study we, investigated the historical variability of disturbances in four different sites in southern boreal forests of Russian Karelia. The target was to determine the disturbance frequency, intensity and range in different spatial scales (plot, site/stand, regional). Also the connection between disturbance quality and forest characteristics was explored. To gather field data and extract increment cores from canopy trees, we established altogether 14 sample plots in four different sites (3-5 per site). We used standard dendroecological methods to record growth releases and gap recruitment from individual trees, indicating past disturbance. With this information, we reconstructed the disturbance chronologies for all plots and sites from the past two or three centuries. From the studied forest sites, two were spruce-dominated stands and one pine-dominated stand. One stand represented mixed-forests with quite an even mix of pine, larch, spruce, and birch trees. The age structure of the forests was uneven-aged in three of the sites. As an exception was the pine-dominated site with relatively even-aged trees (80-100 years). The disturbance chronologies showed significant variation in spatial and temporal scales between sites and sample plots. During the last three centuries (22-26 decades of observation), all the sites had low (0-20%) to moderate (20-40%) or low to high severity (>40%) disturbances. All the sites had gone through a stand-scale disturbance, but no evidence on regional scale disturbance was found. There was no clear connection between forest characteristics and disturbance quality, albeit the data was too small to detect any strong interdependence. The disturbance dynamics showed remarkable variability in disturbance frequency, intensity, and range. The results emphasize the natural heterogeneity and variance related to forest structure, composition and disturbance history. These results back up the prior understanding of the disturbance regime in the Karelian region.